This invention relates generally to polymerization of branched polymers, and, more particularly, to a method of preparing very high molecular weight branched polymers and to the resulting high molecular weight branched polymers.
Since the first dendrimer synthesis was reported in mid 1980""s, dendritic polymers including dendrons, dendrimers, dendrigrafts, and random hyper-branched polymers have quickly been recognized as the fourth major molecular architecture, which exhibits very different properties over the traditional linear, branched, and crosslinked polymers. For example, the dendritic polymers posses smaller sizes, lower viscosities, higher number of surface functional groups, faster reaction kinetics, and controlled interior void spaces when compared with their linear counterparts. The well defined dendrons, dendrimers, and dendrigrafts are normally prepared through a stepwise synthetic process, which often makes them too expensive to be utilized in most of the industrial applications. The cheaper dendrimer analogs, random hyper-branched polymers, have mostly been prepared through polycondensation of ABx monomers (x is 2 or greater). However, due to difficulties associated with condensation reactions, the molecular weights (MWs) of these polymers were generally low, and new monomer syntheses were often required. Very recently, Frechet and his coworkers have developed a self-condensing vinyl polymerization approach, in which an AB monomer having both an initiating center and a propagating center was utilized to produce random hyper-branched polymers. Since each AB monomer has an initiating center, a large amount of initiators (equivalent to monomers) had to be utilized in this polymerization.
This invention pertains to a method of preparing ultra-high molecular weight dendritic polymers in which the branching junctures are assembled in situ (i.e., are self-branching) in a convergent manner during polymerization of the monomers. The invention also relates to dendritic polymers prepared in accordance with the method.